Recent evidence obtained in a variety of experimental circumstances suggests that glomerular ultrafiltration and subsequent fluid reclamation by the downstream peritubular capillaries are subject to humoral and neural regulation. The evidence for this previously unrecognized function of hormones and nerves necessitates an intensive investigative effort to determine their roles in the altered glomerular and proximal tubular function seen in many physiological and pathophysiological conditions. Accordingly, this research project is aimed to 1) clarifying further the kinetics of the processes of glomerular filtration and proximal fluid reabsorption and the mechanisms by which hormones and neurotransmitters affect these processes, and 2) identifying the functional roles of hormones in altered fluid filtration and reabsorption in various physiological and pathophysiological conditions. Using in vivo micropuncture techniques, transcapillary Starling forces determining the filtration and reclamation of fluid will be measured during experimentally induced variations in filtration and reabsorption to ascertain the specific sites and modes of alteration in filtration and reabsorption of the glomerular and peritubular microcirculation. Since hemodynamic alterations induced by some vasoactive hormones are potentially capable of increasing the transglomerular passage of macromolecules, a causal relationship between such hormones actions and proteinuria will also be explored. When appropriate, morphometric techniques will be used to correlate structural and functional observations.